In a gasoline powered car, when driving up a mountain, you use more gasoline per mile driven up, and much less per mile driven down. Driving uphill can use twice the fuel of a level drive, sometimes more than double. The drive downhill uses just enough fuel to keep the engine running, but not to generate motive power. Driving up and then down the same mountain uses about 25% to 50% more fuel than driving on a level roadway.
In an
electric car, the numbers change and it can be quite confusing. The speed you travel downhill has much to do
with whether you can recover any energy or simply use nearly no energy. Typically, driving uphill uses three times
the electricity of driving on a level surface.
But, driving downhill can regenerate electricity, or at the very least,
use very little energy along the way.
The speed you travel downhill has a lot to do with whether you will
regenerate or coast. At freeway speeds,
the effect of wind drag will generally slow the car sufficiently so that you
won’t be able to activate the regenerative brakes (without disrupting
traffic). So, on freeways you will
generally coast downhill, which is like driving for free. At speeds between 10 to 45 MPH, the wind drag
is much less effective at slowing the car, so engaging the regenerative brakes
will be needed, generating electricity that you can use later. (Below 10 MPH, the wheels aren’t turning fast
enough to generate a meaningful flow of electricity.) I find the I can recover as much as 30% of
the electricity that was used to climb the mountain.
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| Using gasoline, there is no energy recovery going downhill like there is with electric drive. |
This means
that much of the uphill penalty is erased when driving downhill (slower than 45
MPH) as electricity is returned to the battery.
In essence, you use less electricity to drive up and then down the
mountain than you use to simply drive up the mountain. But, when planning, you need to ensure that
you have the extra energy to make it up the mountain or you won’t make it to
the downhill side.
Keep in
mind that if you charge fully atop the mountain, then you will have no battery
capacity to capture energy from the regenerative brakes (which prevents them
from working) and you will have to rely on the friction brakes to slow the
car. While you can’t recover electricity
in this case, you still coast downhill using only tiny amounts of energy. It’s better to charge to 85% atop the
mountain.
